Address a bunch of clang-tidy complaints.

There were a bunch more unreasonable/incorrect ones, but these ones
seemed legit. Nothing very interesting, though.

Bug: N/A
Test: ran tests, benchmarks
Change-Id: If66971194d4a7b4bf6d0251bedb88e8cdc88a76f
diff --git a/libc/private/KernelArgumentBlock.h b/libc/private/KernelArgumentBlock.h
index 68d4999..747186c 100644
--- a/libc/private/KernelArgumentBlock.h
+++ b/libc/private/KernelArgumentBlock.h
@@ -32,7 +32,7 @@
 // constituents for easy access.
 class KernelArgumentBlock {
  public:
-  KernelArgumentBlock(void* raw_args) {
+  explicit KernelArgumentBlock(void* raw_args) {
     uintptr_t* args = reinterpret_cast<uintptr_t*>(raw_args);
     argc = static_cast<int>(*args);
     argv = reinterpret_cast<char**>(args + 1);